Package substrates are commonly used for bonding device dies thereon. Package substrates may be used as a buffer for connecting device dies to printed circuit boards and as a routing device. In addition, a plurality of device dies may be bonded to the same package substrate and connected through the package substrate, hence increasing the number of device dies in the respective package.
Some of the package substrates such as coreless substrates are soft and can easily subject to warpage. In the bonding of device dies to these types of package substrates, solder may not be able to attach to the metal traces, resulting in failure to bond.